Abstract
Introduction: This multi-centre observational study explored the impact of unilateral cleft lip conditions on the features of smiles and their relationship with a clinical outcome, biomechanical properties of lips, and psychosocial factors.
Methods: Adolescents and adults (N=42) were recruited from around New Zealand and formed two study groups: a unilateral cleft lip group (N=21) and a non-cleft control group (N=21) matched for age, gender, and ethnicity. All study participants watched an amusing video while their facial expressions were recorded. Smile episodes were automatically detected via software to measure six variables: frequency of smiles, mean duration of smiles, relative smile time percentage, smile genuineness, smile intensity, and tooth show. The cleft clinical outcome was assessed using the Asher-McDade (AM) nasolabial score based on facial photographs. Biomechanical properties of the perioral muscles and cleft scar were measured using myotonometry. Smile Esthetics-related Quality of Life (SERQoL), Orofacial Esthetics Scale (OES), and personality (IPIP-NEO-60) questionnaires were assessed in all study participants.
Results: The features of smiles and personality traits did not differ between the two study groups. Participants in the cleft group exhibited higher stiffness (+44.2%; Cohen’s d = 1.6) and tone (+22.6%; Cohen’s d = 1.9) at the cleft site, along with increased decrement (inverse of elasticity; +8.5%; Cohen’s d = 0.8) at the adjacent perioral site. AM scores and decrement of the cleft scar were both negatively correlated with duration of smiles (R = -0.52 and R = -0.44; p < 0.05) and relative smile time percentage (R = -0.50 and R = -0.49; p < 0.05). Participants in the cleft group had lower scores for the OES as well as higher impacts in the SERQoL in the domains of social contacts and dental self-confidence.
Conclusions: Individuals who have completed treatment for cleft lip exhibit similar smile behaviour as their cleft-free peers - at least in non-social settings. Cleft clinical outcomes and biomechanical properties of lips are associated with propensity to smile. Cleft conditions negatively impact smile-related quality of life, as well as an individual’s perception of their facial appearance in the long term.